The present invention relates to valve seals for internal combustion engines and, more particularly, to an improved structure for a valve stem seal assembly.
Internal combustion engines have a plurality of intake and exhaust valves, each comprising a valve head and a stem reciprocally mounted in a valve guide. The guide height is often imprecise, since precise tolerances would require special machining which increases the cost of the engine. However, inadequate sealing caused by tolerance variations may result in excessive oil consumption. Since the valve stem ordinarily operates in a substantial volume of oil, efforts have been directed toward a decrease in the amount of oil consumed by the engine.
In order to reduce oil consumption and exhaust emissions, and to prevent carbon build-up valve seals have been mounted on valve guides and about valve stems to meter the amount of oil flowing between the stem and the guide. Since valve seal durability is dictated by the choice of sealing rubber, premium fluoroelastomer, which has exceptional physical properties, is often the material of choice for sealing elements. However, fluoroelastomer is very expensive, making rubber the major cost in valve stem seals.
It is seen then that there exists a need for an improved valve stem seal assembly which minimizes the use of rubber and which is capable of being adjusted for imprecise guide height tolerances.